(a) Field of the Invention
Broadly speaking, this invention relates to continuous wave radar systems. More particularly, in a preferred embodiment, this invention relates to a continuous wave radar system in which the CW signal is simultaneously sinusoidally frequency-modulated and pseudo-random phase-modulated.
(B) Discussion of the Prior Art
As is well known, a pulse-modulated radar system is subject to certain inherent limitations, particularly when the Doppler frequency of a moving target is to be ascertained. Continuous wave radar systems overcome these deficiencies but have difficulty in measuring the range of and accurately resolving a target. Also, due to the variation of target echo strength with the fourth power of range, nearby signals can drown out more distant ones.
U.S. Pat. No. 3,396,392, which issued Aug. 6, 1968, and U.S. Pat. No. 3,195,129, which issued on July 13, 1965, both to William Fishbein and Otto Rittenbach, separately solve both of these problems, but in a practical radar system both problems arise simultaneously. A further complication is the interference that occurs between the broadband and narrow-band waveforms as well as the interference that occurs between the target Doppler frequency and the spectral components of the broad and narrow-band signals. All of these problems are compounded when it is desired to use a common transmitting and receiving antenna aperture, for example, in a portable radar system.